Method of making a casting



March 3, 1964 KUENY 3,122,822

METHOD OF MAKING A CASTING- Filed March 31, 1960 INVENTOR KENNETH E.KUENY BYQMW ATTORNEY5 United States Patent 3,122,322 METHOD OF MAKlNG ACASTING Kenneth E. Kueny, North Muslregon, Mich, assignor to JohnsonProducts, Inc, Muskegon, Mich a corporation of Michigan Filed Mar. 31,1960, Ser. No. 18,894 1 Claim. (Cl. 29-1563) This invention relates to amethod of making a valve tappet, and more particularly to a specificmethod of casting a valve tappet.

For a long time valve tappets have been cast from a metal such ashardenable iron. in casting the valve tappets, the outer edge portion ofthe valve tappet foot becomes chilled before the central portion of thetappet foot. This is true since the heat from the molten metal istransferred into both the foot and side portion of the mold. Quickchilling brings about a desirable effect in the valve tappet in that aneedle-shaped constituent, acicular carbide, is formed in the quickchilled area of the tappet. This form of carbide formation is desirablesince it provides a hard wearing surface and has certain lubricouscharacteristics.

Since it is desirable to have the total surface area of the valve tappetfoot contain acicular carbides, it is necessary to provide some meanswhereby the central portion of the valve tappet foot may be chilled asquickly as the edge portion. Applicant has solved this problem byproviding the mold with pin forming depressions in the central area ofthe valve tappet foot mold. Thus, when the metal is poured it will flowinto these depressions causing pins to be formed which project from thefoot surface. This greatly increases the surface area from which heatmay be radiated and provides a means whereby the center portion of thevalve tappet foot surface may be chilled as rapidly as the outer edge.This results in a formation of acicular carbides throughout the entiresurface area of the valve tappet foot.

The valve tappet formed in this manner can be readily machined beforethe heat treating process. A simple grinding operation removes theprojecting pins from the foot of the valve tappet. The valve tappetproduced by the method disclosed herein provides a tappet which isreadily machinable but after heat treatment provides a foot surfacewhich is extremely hard and resistant to wear.

it is an object of this invention to provide a method of casting a valvetappet wherein the total foot surface area is chilled.

Another object of this invention is to provide a method for castingvalve tappets wherein the central portion of the foot surface isprovided with projections or pins to increase the total surface coolingarea.

A further object of this invention is to provide a valve tappet whichhas good machining properties and a foot area with good wearcharacteristics.

Still another object of this invention is to provide a method of makinga valve tappet wherein the total foot surface area contains a formationof acicular carbide.

These and other objects and advantages in the practice of this inventionwill be more apparent in the illustrations and description of a workingembodiment of the invention as hereinafter set forth.

'In the drawings:

FIG. 1 is a cross section view of a valve tappet showing the formationof acicular carbide when a previous method of casting has been employed;

FIG. 2 is a cross sectional view taken along the section line IH-III ofFIG. 3 and showing the acicular carbide formation in a valve tappetfollowing the method of casting of this invention.

FIG. 3 is a perspective view of the valve tappet of this invention shownas removed from the mold.

This invention relates basically to a method of casting a valve tappet.

This method is practiced by providing a foot surface of a conventionalvalve tappet mold, with pin forming depressions. Hardenable iron isheated to pouring temperature and poured into the mold. As the moltenmetal comes into contact with the surface areas of the mold, it ischiilled or cooled rapidly in the lower portion of the mold or vicinityof the valve tappet foot surface. Rapid heat radiation takes place aboutthe outer edge of the foot surface, since the bottom and side edges ofboth are exposed to the mold providing for radiation in both directions.The efiective surface area of the central portion of the foot surface isincreased by the projections formed thereon. The heat is transferredfrom the central portion of the foot surface to the projections and thusinto the mold. The proiections provide enough added heat transferringarea so as to cause the central portion of the valve tappet foot area tocool at approximately the same rate as the outer edge, thereby formingthe desirable acicular carbide formation over the en tire valve tappetfoot surface area.

Reference is now made to the drawings wherein the valve tappet of thisinvention is shown in FiG. 3 and designated generally as 10.

The valve tappet 10 as it comes from the mold subsequent to castingtakes the shape as shown in FIG. 3. The valve tappet 10 has acylindrical outer surface 11 and an end or foot surface 12. Projectionsor pins 13 extend from the central portion of the foot surface. Theopposite end of the valve tappet has a stem 14 projec"- ing therefromformed during the casting process and later removed during the grindingoperation.

The tappet It} is cast in a conventional sand mold shown generally as 29in FIG. 2. The sand mold 29 has pin forming depressions 21 in the footsurface thereof. Otherwise the mold is similar to the mold 3% previouslyused and shown in FIG. 1.

The valve tappet It as shown in FIG. 3, which forms the subject of thisinvention, and the valve tappet 35 as shown in FIG. 1, which shows avalve tappet previously in use, are both preferably manufactured fromhardenable iron of approximately the following composition: carbon3.0%3.4%, silicon 2.-l0%2.40%, manganese .70%-.90%, sulphur 10% maximum,phosphorus 20% maximum, nickel .40%.70%, chromium .9l%1.25%, molybdenum.40%.7G% and the remainder iron. Hardenable iron as cast is composed offlake graphite pearlite and carbides, the latter appearing in acicularform at quick chilled points of the casting, and in cellular form wherethe cooling is gradual.

An acicular carbide formation is desirable in the foot surface area ofthe valve tappet. When the valve ta et is cast in a mold such as a mold30, the acicular carbide formation takes place approximately as shown inFIG. 1. The acicular carbide 31 forms in the lower outer cylindricalsurface and the outer edge of the foot surface of valve tappet 35. Thecentral portion 32 of the valve tappet 35 foot surface does not containacicular carbide but forms into a cellular carbide formation. Thecellular carbide formation is not desirable for valve tappet footsurfaces, since upon heat treatment it does not produce the hard wearingsurface as does acicular carbide.

In view of the fact that in previous casting methods the center portionof the valve tappet foot surface has cooled slower than the outer edgesthereof, the present method has been devised. This new method produces avalve tappet foot surface which has an acicular carbide formation acrossthe entire or total surface area of the foot of the tappet. This isaccomplished by providing the mold, such as 20, with pin formingdepressions 21 in the foot surface area of the mold. The number ofdepressions necessarily. vary with the diameter of the valve tappet. Thelarger the diameter the more projections or pins needed to convey theheat to the mold. By providing the foot surface area of the mold withthe pin forming depressions the total surface area of the center portionof the tappet is increased considerably. By adding the chill pins 21 tothe valve tappet 1%, the surface area exposure of the center portion ofthe valve tappet foot is approximately the same as the outer cylindricalsurface of the valve tappetin combination with the outer edge of thefoot surface area. Thus, the entire foot surface area cools or ischilled at approximately the same rate. This provides an acicularcarbide formation throughout the entire foot surface area. This is bestshown in FIG. 2 by the particular carbide formation designated as 15.The degree of penetration of the acicular carbide formation into thebody of the valve tappet depends upon the rate of chill and variessomewhat from mold to mold. However, a sufiicient layer results so as toallow grinding off the pins or pro- 7 jections 13 and leaving a layersufficiently thick to provide a hard wearing surface.

7 The valve tappet 1% as cast is composed of a grain structure ofgraphite, pearlite and carbide. The body portion 16 of the. valve tappethas a cellular carbide formation, and the foot surface area 15 has anacicular carbide formation, these two carbides being interspersed withthe graphite and pearlite in the respective areas. The pins 13 areground from the foot surface while the valve tappet is in this form ofgrain structure. Other necessary machining is also done at this time.

After the tappet has been machined to the proper dimensions, it is heattreated. Heat treatment is accomplished by a conventional mannerbringing the tappet to a temperature of approximately 1550 degreesFahrenheit to 1570 degrees Fahrenheit. Upon completing the heattreatrnent, the pearlite grain structure is transformed to martensite.The graphite and carbide structures rernain unchanged.

The above method produces a valve tappet which has a very hard footsurface. This hardness is approximately 55 to 61 Rockwell C. A wearingsurface of at least this hardness is desirable for a valve tappet foot.

The tappet of this invention having an acicular carbide formation acrossthe entire foot surface of the tappet is far superior to the tappetwhich has such a formation only around the outer edge thereof. Thus,where tappets previously had the tendency to wear in the center portionthereof, this tendency has been reduced to a minimum, since the samegrain structure of the tappet is presented over the entire foot surfacearea.

These desirable features in the valve tappet have been accomplished bymerely providing the conventional mold with pin forming depressionslocated near the center portion of the tappet foot surface area. Thesedepressions allow pins or projections to form on the surface of thetappet foot, providing means of quick heat transfer from the moltenmetal to the molds. The center portion of the valve tappet foot iscooled at approximately the same rate as the edges, providing for theformation of the desirable acicular carbide formation throughout thetotal foot surface area. The same grinding operation which previouslyground a foot surface of a valve tappet such as 35 can be used to grindthe foot surface of the valve tappet 1%. Therefore, the pins 13 requireno additional operation for removal. The pin forming depressions 21 canbe formed in the mold by a pattern as easily .as the previous type moldused. Thus, it can be seen that applicants method produces a valvetappet which is far superior and yet can be manufactured at no addedexpense. Thus, applicants method produces a valve tappet which is highlydesirable com mercially.

While a preferred embodiment of this invention has been described, itwill be understood that modifications thereof may be made. Such of thesemodifications as incorporate the principles of this invention are to'beconsidered asindicated in the hereinafter appended claim unless thisclaim by its language expressly states otherwise.

I claim: I

The method of making a Valve tappet comprising the steps of: forming a.valve tappet mold having a cavity with one wall thereof comprising afoot forming surface; providing the foot formingsurface with pin formingdepressions intermediate the outer edge of said foot forming surface;heating hardenable iron to a pouring temperature, pouring and chillingsaid hardenable iron into said cavity thereby forming a casting with afoot surface having pins extending therefrom intermediate the outeredge, said pins providing means for dissipating heat from saidintermediate section thereby increasing the coolin rate of saidintermediate section to form an acicular grain structure; and machiningsaid pins down flush with the foot surface.

References Cited in the file of this patent UNITED STATES PATENTS1,318,748 Hadfield Oct. 14, 1919 1,560,832 Lee Nov. 10, 1925 2,096,092Dostal Oct. 19, 1937 2,134,749 Burt Nov. 1, 1938 2,143,410 Dornin Jan.10, 1939 2,273,551 Zweier Feb. 17, 1942 OTHER REFERENCES Principals ofMetal Casting, Heine and Rosenthal,

